Control of Pattern Specific Corrosion During Aluminum Chemical Mechanical Polishing
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CONTROL OF PATTERN SPECIFIC CORROSION DURING ALUMINUM CHEMICAL MECHANICAL POLISHING Hyungjun Kim, Panki Kwon, Sukjae Lee, Hyung-Hwan Kim, Sang-Ick Lee, Seo-Young Song, and Chul-Woo Nam Memory R&D Division, Hynix Semiconductor Inc., Ichon, Korea ABSTRACT A pattern specific corrosion of aluminum wires was found during aluminum chemical mechanical polishing process. This paper presents and discusses the particular pattern dependency of the corrosion behavior and effective control methods in order to reduce the corrosion. An aluminum single damascene structure on silicon dioxide thin film was prepared and the effects of process variables and pattern configuration on corrosion behavior were extensively explored. The corrosion behavior was quantitatively analyzed using sheet resistance of corroded line. It was demonstrated that corrosion of aluminum wire was associated with cleaning media and pattern configuration. The area ratio between sub-micron size line and pads was the most important factors to determine the corrosion behavior. A post cleaning chemical including corrosion inhibitor couldn’t prevent the corrosion perfectly. It was found that sacrificial dummy lines could reduce the aluminum corrosion, which suggests that the aluminum corrosion could be controlled by the structural consideration in aluminum damascene. INTRODUCTION Aluminum damascene technology as an alternative to aluminum RIE process has been widely investigated at least in some DRAM industries, where the introduction of Cu process is yet questionable. Chemical mechanical polishing (CMP) is a key process technology in aluminum damascene. Due to insufficient process maturity of Al CMP in comparison with another metal CMP, there are many issues not fully understood. As previously reported [1,2], corrosion phenomenon of aluminum after CMP is one of them. Aluminum corrosion results in high line resistance as well as the reduction of interconnect reliability. It has not been observed during polishing, but during post polish step, such as buffing, post cleaning, etc., which include the step to rinse wafer with deionized water (DIW). Since aluminum is chemically very active material, corrosion is observed even during the wafer transfer in wet state within CMP tool. This corrosion showed a pattern dependence. Narrow line of sub quarter micron size connected to large bond pad could be easily corroded while wide line or floating one showed clean polished surface. In the present study, a pattern dependence of aluminum corrosion was investigated using a specially designed test vehicle. Corrosion behavior of aluminum wires was quantitatively characterized with the structural variation. Concepts of sacrificial dummy were tried to reduce corrosion in the structural point of view. Van der Pauw test structures were employed to measure the sheet resistance from which the amount of aluminum loss caused by corrosion was calculated in accordance with corresponding structural conditions. EXPERIMENTAL An aluminum single damascene structure on silicon dioxide thin film was
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